What important item did Napoleon bring back from Egypt? What was the significance?

The Napoleonic Invasion of Egypt started in 1778. The invasion included 400 ships and over 50,000 men, 150 of whom were scholars and scientists.

The most notable artefact that was captured was the Rosetta Stone. To this day, the Rosetta Stone is one of the most important artefacts ever discovered in Egypt.

The Stone, which is about one metre tall (although it is broken at the top), has scripts in Greek, Egyptian demonic and hieroglyphics. The text specifies that each script is an exact copy:

“This decree shall be inscribed on a stele of hard stone in sacred [i.e., hieroglyphic] and native [i.e., demotic] and Greek characters and set up in each of the first, second and third — [rank] temples beside the image of the ever-living king.”

The Stone therefore acts as a translation device. This purpose was quickly identified by the French discovers - who were fluent in Greek.

The Stone is the basis from which all hieroglyphics were translated. Understanding of the graphical language, which had been dead for ~2000 years, reinvigorated studies of ancient Egypt.